The initiation of the autoimmune process in myasthenia gravis (MG) remains enigmatic. Our investigations are directed toward obtaining more information about the source of the break in tolerance which results in autoimmunity. D-Penicillamine MG provides a unique opportunity to investigate mechanisms by which this drug initiates MG and the basis for the reversibility of disease when the drug is stopped. We have shown that D-pennicillamine (D-Pen) can bind to and alter AChR function in vitro and that immunization of rabbits with D-Pen-AChR generates antibodies that recognize D-Pen as a hapten. Chronic D-Pen administration to Strain A mice augments initiation of anti-AChR and experimental myasthenia. We now plan to determine whether or not T cells from Strain A mice and humans with D-Pen MG recognize D-Pen as a hapten or as a helper determinant and whether they are sensitized to D-Pen or to D-Pen-AChR to a greater extent than AChR alone. We will pursue investigations of the significance of the abnormal thymus gland in the development of autoimmune MG. Myoid cells containing the major autoantigens exist, by immunocytochemistry, in the reticulo-epithelial cell population of the thymic medulla in normal young animals and in myasthenic glands from patients at all ages. Thymic epithelium, bearing IA antigens crucial to initiation of recognition of "self", can be established in culture as can myotubes from muscle and thymus and possibly from thymic myoid cells. We plan to examine the ability of thymic epithelium to potentiate not only maturation, but possibly sensitization of naive T cells to muscle antigens, using purified proteins and muscle in culture to present these antigens, and assaying for T cell proliferative responses and surface differentiation antigens. We will investigate for the presence of Ia on muscle, muscle in culture and myoid cells. We will also evaluate the ability of myasthenic thymic epithelium from patients with different thymic pathology (normal, hypeplasia, involution, thymoma) to grow in culture and to express Ia antigens, in comparison to the presence and status of myoid cells in these glands.